Internal gear pumps equipped with the aforementioned pump rotor in which the difference in the number of teeth is one are widely used as oil pumps for vehicle engines or for automatic transmissions (AT). Patent Literatures (PTLs) 1 to 3 below disclose examples of such an internal gear pump in the related art.
In an internal gear pump disclosed in PTL 1, tooth profiles of an inner rotor and an outer rotor are each formed by using a base circle, a locus of one point on an externally rolling circle that rolls in contact with the base circle without slipping, and a locus of one point on an internally rolling circle.
In an internal gear pump disclosed in PTL 2, addendum and dedendum cycloidal tooth profiles are formed by using two base circles having different diameters, an externally rolling circle that rolls in contact with one of the base circles without slipping, and an internally rolling circle that rolls in contact with the other base circle without slipping, and the addendum and dedendum cycloidal tooth profiles are connected with each other by using an involute curve.
In an internal gear pump disclosed in PTL 3, a tooth profile of an outer rotor is formed by using a convexed arc curve or a cycloidal curve. Then, a tooth profile of an inner rotor is determined by rolling the inner rotor within the tooth profile of the outer rotor.
In addition to these examples, an internal gear pump that uses a trochoidal-curve tooth profile is also known.